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SOME EXPERIMENTS WITH A 

BORIC-ACID CANNING 

POWDER 



RUTH B. EDMONDSON, CHARLES THOM, 
AND L. T. GILTNER 



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UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT CIRCULAR 237 



Washington, D. C. 



Issued August, 1922 



WA8HINQTON : GOVERNMENT PRINTINO OFFICE : 1921 



BffonogTapij 



uiSTarv of~conu*ess 
UU.l 1 1929 

DOCUMENTS DIVISION 



SOME EXPERIMENTS WITH A BORIC-ACID 
CANNING POWDER. 

By Ruth B. Edmondson, Assistant Mycologist, and Charles Thom, Mycologist 
in Charge, Microbiological Laboratory, Bureau of Chemistry, and L. T. 
Giltnee, Veterinary Inspector, Bureau of Animal Industry. 



Page. 

Canning powder examined 1 

Antiseptic value of powder 2 



CONTENTS. 

Page. 



Discussion of results 9 

Summary 11 



CANNING POWDER EXAMINED. 

Among the many inquiries concerning canning problems received 
by the microbiological laboratory of the Bureau of Chemistry, in- 
formation as to the use of " canning powder " to supplement heat in 
processing has been frequently sought. These requests come from 
places widely enough separated to indicate that propaganda for the 
introduction of some sort of antiseptic in the home preservation of 
food is fairly widespread. 

Specific inquiries supplemented by samples obtained for analysis 
indicated the use of a particular preparation in many sections of 
the country. Several series of packages of this preparation, there- 
fore, were secured for study. Each package consisted of an envelope 
of white powder bearing printed directions for use. To furnish a 
basis for intelligent work one series of packages was analyzed. 1 The 
powder consisted of approximately 95 per cent of boric acid and 
5 per cent of common salt, the actual divergences from this average 
being about one-half per cent in either direction. The net weight of 
36 envelopes averaged 28.97 grams, with a minimum of 25.22 and a 
maximum of 34.89 grams. Evidently each package was intended to 
contain 1 ounce (28.34 grams) of powder. At the minimum content 
found, however, the loss of antiseptic power might be great, while at 
the maximum content the excess of toxicity might be serious. 

The directions given on the envelopes of powder called for the use 
of one-fourth package (one-fourth ounce) to each quart of finished 
material, and provided a means for the rough division of the powder 
into fourths. No suggestion that the use of an excess of the canning 
powder might be harmful was offered. Considering the difficulty of 

1 The chemical work was done by J. I. Palmore, of the food control laboratory of the 
Bureau of Chemistry. 

111612°— 22 1 



2 Department Circular 237, U. S. Dept. of Agriculture. 

estimating how much bulky fresh material would make a quart of 
finished or canned material, together with the haphazard method of 
measuring the powder and the wide range of variation found in the 
contents of the packages, the quantity of the canning powder actually 
used in successive lots of food would be variable enough to lower 
its antiseptic value, or, possibly, if in excess, to affect the consumer. 

ANTISEPTIC VALUE OF POWDER. 

TEST-TUBE EXPERIMENTS. 

To obtain some measure of the antiseptic value of the powder at 
the minimum, average, and maximum concentrations, as indicated by 
the actual content of the packages, standard culture media were 
made containing the canning powder in such quantities as to make 
a concentration of 0.63, 0.724, and 0.872 per cent (one- fourth package 
per quart), respectively. These were inoculated, together with con- 
trols on the same media without the powder, with cultures of various 
bacteria and a yeast. Daily observations of the cultures were made 
for a period of one week. The organisms chosen (Table 1) represent 
certain large groups commonly found in contaminated or spoiled 
products and are significant in considering the soundness or safety 
of food supplies. 

Table 1. — Bacteria and yeast used for inoculations. 

ORGANISM. SOURCE. 

Bacterium aerogenes Italy. 

Bacterium coli Fecal strain from 

ripe olives. 

Bacterium enteritidis Jordan. 

Bacterium paratyphasum A Mears. 

Bacterium paratyphosum B Rowland. 

Bacterium typhosum Mears. 

Bacterium suipestifer Krumwiede. 

Proteus vulgaris Rettger. 

Staphylococcus aureus Rettger. 

Streptococcus lacticus Ayers. 

Streptococcus pyogenes Rettger. 

Bacillus mesentericus ruber Le Fevre. 

Bacillus mesentericus niger ___. Le Fevre. 

Bacillus subtilis Le Fevre. 

Bacillus botulinus Type A Boise strain. 

Bacillus botulinus Type A Memphis strain. 

Bacillus botulinus Type B " District " strain. 

Bacillus sporogenes ___. Savage. 

Bacillus sporogenes Mullet strain. 

Bacillus putrificus Rettger. 

Bacillus stear other mopliilus = Donk. 

Bacillus bulgaricus + - Sherman. 

Bacillus acidophilus Rettger. 

K 5 (bacillus from pickle brine) Le Fevre. 

Pink yeast Hunter. 



A Boric- Acid Canning Powder. 3 

At the minimum concentration (0.63 per cent) the canning powder 
exhibited a selective antiseptic action on the growth of these or- 
ganisms. Of the 25 organisms tested the powder prevented the 
growth of but three (the yeast, Pro tern vulgaris, and B. stearo- 
thermophilus) . All but one (B. stearothermophilus) of these three 
are aerobic and non-spore- forming and would be killed in any ordi- 
nary process of canning. The behavior of B. bulgaricus, B. acido- 
philus, and the pickle bacillus is interesting. Their growth was 
prompt, while that of Streptococcus lacticus was inhibited until the 
fourth day. The growth of the remaining organisms was but 
slightly less abundant on this medium than on the control. It is 
significant that not only was the growth of none of the resistant 
anaerobic spore-forming bacteria stopped by the powder, but in the 
medium containing the powder it was as luxuriant as in the control 
medium. The toxin-producing power of B. botulinus makes this 
especially important. 

With the average concentration of the canning powder (0.724 per 
cent) the results were similar to those obtained with the minimum 
concentration, in that the growth of certain of the aerobic organisms 
(B. mesentericus niger, Bad. aerogenes, Bad. typhosum, Bad. para- 
typhosum A and B,. Staphylococcus aureus, Streptococcus lacticus, 
the yeast, and B. acidophilus) was slightly inhibited and that of a 
few (B. subtilis, Proteus vulgaris, Bact. coli, B. stearothermophilus, 
Bact. enteritidis, and Bact. suipestifer) was entirely prevented. The 
resistant anaerobic species, however, were not affected, even to the 
extent of having their growth noticeably checked. 

Practically the same results were obtained at the maximum con- 
centration (0.872 per cent), except that more of the aerobic or- 
ganisms (B. mesentericus niger, B. subtilis, B. stearothermophilus, 
B. acidophilus, Bact. typhosum, Proteus vulgaris, and the yeast) 
were checked and those that were not (B. mesentericus ruber, Bact. 
aerogenes, Bact. coli, Bact. enteritidis, Bact. suipestifer, Bact. para- 
typhosum A and B, Streptococcus pyogenes, Streptococcus lacticus, 
Staphylococcus aureus, B. bulgaricus, and the pickle organism) grew 
more slowly than at the lower concentrations. As before, the 
anaerobic species were not affected by the presence of the canning 
powder. 

Fifteen cultures (B. mesentericus niger, B. mesentericus ruber, 
B. subtilis, Bact. aerogenes, Streptococcus pyogenes, Proteus vul- 
garis, Bad. typhosum, Bact. coli, the yeast, B. stearothermophilus, 
2 strains of B. sporogenes, and 3 strains of B. botulinus) were tested 
with three times (2.172 per cent) the average concentration (0.724 
per cent) of canning powder recommended, with the result that the 
growth of all but two (B. mesentericus ruber and Bact. aerogenes) of 



4 Department Circular 237, U. S. Dept. of Agriculture. 

the organisms was prevented, and the growth of these two was 
meager and slow. 

Since the growth of B. botulinus was not inhibited in the forego- 
ing experiments by the minimum, average, or maximum concentra- 
tion of the canning powder, a standard medium containing the 
powder in concentrations varying from 0.8 to 2 per cent was made, 
and a number of strains of B. botulinus (Laboratory Nos. 619, 621, 
622, 623, 626, and 629, respectively) and B. sporogenes (Savage and 
Mullett)were grown in it. Daily observations were made as before 
for a period of two weeks. None of the B. botulinus strains were 
prevented from growing by even 1 per cent of the canning powder. 
One strain (619) grew slowly at that concentration, but growth was 
clearly evident on the ninth day after inoculation. Two strains (623 
and 626), which grew in the presence of 1.5 per cent of the powder, 
did not begin to grow until the fourth day. The B. sporogenes 
strains grew well at this concentration. A concentration of 2 per 
cent, however, restrained all the B. botulinus strains, as well as the 
B. sporo genes strains. Although these concentrations are much 
higher than those advocated for use in actual canning, the results 
obtained with them are significant in that any sense of safety from 
food poisoning founded on the use of the antiseptic is groundless, 
and dependence on it becomes a source of danger. 

A similar series of cultures was made to test the effect of canning 
powder upon a group of molds. Tubes of dextrose agar to which 
the canning powder had been added in percentages of 0.63, 0.724, 
and 0.87 were prepared and inoculated, together with controls on the 
same medium without canning powder. 

For this purpose the following molds were used : Penicillium brevi- 
caule, P. camemberti, P. roqueforti, P. divaricatum, P. spinulosum, 
P. viridicatum, P. oxalicum, P. expansum, Aspergillus fiavus, A. ni- 
ger (2 strains), A. oryzm, A. fumigatus, A. terreus, A. nidulans, 
A. sydowi, A, repens, Acrastalagmus cinnabarinus, C ephalothecium 
roseum, Trichoderma lignorum (?), one species of Rhizopus, De- 
matium, and Syncephalastrum sp., and three strains of Cladosporium. 

Observations were made at the end of 3, 6, 11, and 17 days. The 
control cultures showed the usual colonies characteristic of each 
species. Twelve of these strains showed growth, but every one of 
them was delayed in development by the canning powder. Of these, 
Aspergillus niger, A. terreus, Penicillium camemberti, and Dematium 
eventually produced colonies characteristic of the species. Penieil- 
lium spinulosum, representing the Citromyces section of the group, 
P. expansum (the apple rot), P. divaricatum, two strains of Clados- 
porium, and A. sydowi showed more or less growth without produc- 
ing the typical coloring characters within the time of observation. 



A Boric- Acid Canning Powder. 5 

The Acrostalagmus barely showed germination in the lowest concen- 
tration of powder. The other organisms failed to germinate in this 
experiment. In food canning experiments with the powder, how- 
ever, an occasional mold colony was encountered and transferred to 
culture media. In this way Penidllium rogue forti (roquefort cheese 
mold) was once obtained in a cherry, Aspergillus fumigatus from 
tomatoes, A. flavus from peas, and one mucor from peaches. No one 
of these four species grew in the test-tube series of cultures, but A. 
flavus and A. fumigatus grew slowly in another culture experiment 
in the presence of 0.7 per cent of the powder. Clearly, then, the boric- 
acid canning powder in question has a selective effect on molds also, 
both in reducing the number of species which will germinate and in 
delaying or restricting the development of others, but it will not 
entirely eliminate spoilage due to certain common species of mold. 

PRACTICAL CANNING EXPERIMENTS. 

To test the efficiency of the canning powder under practical con- 
ditions, many of the fruits and vegetables in season were canned with 
it according to the directions printed on the packages of the powder 
and given in accompanying literature. To check the efficiency of the 
method of canning recommended, similar materials were canned in 
the same way, omitting the powder, and also by a well-known method. 
Wherever feasible three such series of samples for each product were 
prepared as follows : 

Series 1 : Prepared with the canning powder in accordance with 
directions. 

Series 2 : Prepared as in Series 1, but without the canning powder. 

Series 3 : Prepared by the so-called " one-period cold-pack " method 
(Farmers" Bulletin 829) . 

The method used in Series 1 varies slightly for the different vege- 
tables and fruits, but is essentially that of cooking in the open kettle, 
with the addition of the canning powder at a particular stage in the 
cooking. The point at which the powder is added varies with the 
product and, with the exception of rhubarb, mincemeat, relishes, and 
pickles, is followed by a period of subsequent cooking so as to take 
a reasonable advantage of whatever efficiency the boric acid has as a 
sterilizing agent. 

The products canned 2 were asparagus, cherries, corn, cucumber 
salad, lima beans, mincemeat, peaches, pears, peas, rhubarb, straw- 
berries, string beans, and tomatoes. Materials were obtained in as 
fresh a condition as possible from the Washington City Market and 
were canned as soon as practicable after delivery. Pint glass jars 

2 The canning was done by Mrs. Mabel Heffner of the States Relations Service, U. S. 
Department of Agriculture. 



6 Department Circular 237, U. S. Dept. of Agriculture. 

were used as containers. Rubbers were tested before use, and the 
sealed jars were examined carefully for leaks before the products 
were stored in the basement of the Bureau of Chemistry. 

A number of jars in each series were artificially inoculated with 
bacteria at the time of canning. The bacteria used were B. coli, B. 
aerogenes, B. sub tills ^ B. stearothermophilus, Proteus vulgaris, B. 
botulinus, and B. sporogenes. Several strains of the last two species 
were used. In all, 310 pints of material were canned. Of these 175 
were inoculated. Of the 310 pints canned, 174 were put up with the 
canning powder ( Series 1 ) , and of these 98 were inoculated ; 46 were 
canned as in Series 1, but without the powder (Series 2), and 21 of 
them were inoculated; 90 were canned by the one-period cold-pack 
method (Series 3), and 56 of them were inoculated. 

After being stored for from 1 to 3 months some of the jars of each 
product in each series were opened and examined physically and 
bacteriologically for signs of spoilage. A detailed record of the con- 
dition of each jar was kept. This included the condition of the jar 
and its contents, the H-ion concentration (colorimetric method of 
Clark and Lubs 8 ), the types of bacteria present in the juice of the 
material (as determined by Gram stained smears), and the types of 
bacteria found in aerobic and anaerobic cultures made from the 
material. In all, 177 jars were thus examined. The remaining jars 
that were not opened were examined frequently for physical evidences 
of spoilage, such as gas production, foul odor, and disintegration of 
material. The correlation between these findings and the bacteri- 
ological results was so close that for practical purposes the material 
could be judged as spoiled or not merely by a physical examination 
of the jar. 

The results of the bacteriological examinations are summarized in 
Table 2. The word " spoiled " is applied to those jars in which there 
was an active growth of anaerobic bacteria. Where organisms were 
recovered in cultures from either uninoculated or inoculated jars in 
which there was no evidence of the growth of the bacteria the mate- 
rial was not considered to have spoiled. 

8 Clark, W. M., and Lubs, Herbert A. The Colorimetric Determination of Hydrogen 
Ion Concentration and Its Application in Bacteriology. J. Bact.,, 2 (1917) : 1-34, 109- 
136, 191-236. 



A Boric-Acid Canning Powder. 



Table 2. — Summary of canning experiments. 







Series 1 (with canning powder). 




Product canned. 


Number 
canned. 


Number 
inocu- 
lated. 


Number examined 
bacteriologically. 


Number spoiled. 




Check. 


Inocu- 
lated. 


Check. 


Inocu- 
lated. 


Asparagus 


24 
12 
12 
4 

8 

•! 

8 
14 
24 
24 
20 
12 


16 
6 
9 
2 
6 
2 
5 
5 
8 
12 
12 
7 
8 


6 
2 
1 
1 
1 
1 
2 
2 
2 
8 
9 
8 
2 


10 
4 
5 


6 


10 






Corn 


1 


5 






Lima beans 


3 
1 
4 
3 
4 
7 
7 
4 
5 


1 
1 


3 


Mincemeat 


1 


Peaches 










Peas 


2 


4 




1 






a 1 




5 


4 




4 








Total 


174 


98 


45 


57 


16 


33 











Series 2 (without 


canning powder). 




Product canned. 


Number 
canned. 


Number 
inocu- 
lated. 


Number examined 
bacteriologically. 


Number spoiled. 




Check. 


Inocu- 
lated. 


Check 1 Inocu " 
Lnecj5: - j lated. 














Cherries 


3 
2 
4 
4 
2 
2 


1 
1 
2 
3 


2 

1 
1 






Corn 


1 
1 
3 


1 1 










3 


Mincemeat 


1 




Peaches 


1 


1 




Pears 






Peas 














6 
6 
11 
6 


4 
3 
2 

4 


1 
1 
6 
1 


3 
2 
2 
2 













6 
1 


2 


Tomatoes 


2 






Total 


46 


21 


14 15 


8 8 















Series 3 (one-period cold-pack method). 


Product canned. 


Number 
canned. 


Number 
inocu- 
lated. 


Number examined 
bacteriologically. 


Number spoiled. 




Check. 


Inocu- 
lated. 


Check. 


Inocu- 
lated. 


Asparagus 


14 

8 
10 


6 
4 
6 


4 
2 
2 


4 

2 
2 












Corn 


1 


2 








8 


6 


1 


4 




4 










6 


4 
4 
8 
6 
2 
4 
6 


1 
2 


2 
2 
4 
3 
1 
2 
3 








6 
10 

8 






Peas 


2 


3 




1 
2 
1 






String beans 


8 
8 


1 


1 


Tomatoes 

Total 


1 






90 


56 


17 


29 


4 


11 



The inoculum (B. sporogenes) was added after cooking the product. 



8 Department Circular 237, U. S. Dept. of Agriculture. 

Grouping the products canned, the following conclusions may be 
drawn from Table 2 : None of the fruits canned by the " open-kettle " 
method, with or without the canning powder, or by the " one-period 
cold-pack" method spoiled, with the exception of an inoculated jar 
of strawberries and a few jars of other fruits, in which small mold 
colonies were found. In the case of the strawberries, the inoculum, 
B. sporo genes, was added just before the jar was sealed and the 
product received no subsequent processing. Acid products (Table 3) 
are usually considered to be easily preserved. The keeping of the 
majority of those canned in these experiments, therefore, is but the 
ordinary experience. . 

On the other hand, the more or less neutral products (Table 3) are 
generally accepted as being more difficult to can successfully. In one 
series a total of 78 cans of corn, asparagus, peas, string beans, and 
lima beans were packed with the canning powder, using products 
from the city market. As determined by physical examination, 68 of 
the total number spoiled. Forty- four of the 78 cans put up were 
examined bacteriologically, with the result that 41 showed bacterial 
activity. In another series of 50 cans put up by the so-called " cold- 
pack" method, 14 spoiled. Neither of the methods used, therefore, 
proved adequate to preserve these particular lots of vegetables pur- 
chased in the city wholesale market. It is evident also that the boric 
acid of the canning powder failed to overcome either the natural 
infection or the inoculation added in the laboratory. 

Of the other products studied, tomatoes put up with the canning 
powder but not inoculated remained sound, whereas 4 out of 8 cans 
inoculated spoiled. The tomatoes which received the same cooking 
but no powder spoiled. This gives in the case of tomatoes some sup- 
port to the claim that the addition of the canning powder will permit 
a shortening of the cooking process. Thirty of the jars of rhubarb 
were packed in water without cooking, according to the method 
recommended. Of these 24 contained canning powder, 12 of which 
were inoculated, while 6 were in cold water only. Of these 30 jars 
packed without cooking one inoculated with B. sporogenes spoiled; 
the remaining 29, with and without the canning powder, showed no 
bacterial activity. This result may be fairly attributed to the natural 
acidity of the rhubarb rather than to the powder. Similarly, in the 
cucumber salad and mincemeat the presence of a large quantity of 
vinegar accounts for the absence of spoilage. 

Bacillus botulirms did not grow in any of the fruits canned, but it 
did grow and produce its toxin in most of the vegetables canned. 
Samples of asparagus from Series 1 (with canning powder) and 
Series 2 (without canning powder), which had been inoculated with 
B. botulinus and which showed extensive spoilage on opening, pro- 
duced typical symptoms of botulism and death in guinea pigs fed 



A Boric-Acid Canning Powder. 9 

with 5 cubic centimeter amounts of the juice. There was no growth 
of the organism in asparagus canned by the cold-pack method. B. 
botulinus grew and produced toxin in corn, lima beans, and string 
beans, put up in all three series. The spoilage in these products was 
particularly offensive. Large quantities of gas were formed, the 
liquid spurted when the jars were opened, and the material was 
more or less disintegrated. Peas canned with the canning powder 
and inoculated with B. botulinus proved toxic to guinea pigs, while 
those canned by the cold-pack method were not toxic. Bacillus 
botulinus did not grow in the rhubarb, mincemeat, or cucumber salad 
canned. It did grow in tomatoes canned without the canning powder 
(Series 2) and by the cold-pack (Series 3) method, but not in to- 
matoes canned with the canning powder. The tomatoes were slightly 
overripe when canned, and the addition of the boric-acid canning 
powder in Series 1 evidently protected them. 

These results with B. botulinus in the canning of the so-called 
neutral products, which are in harmony with the results in the test- 
tube experiments, show that the boric-acid canning powder is not 
a safeguard from the type of food poisoning known as botulism or 
from extensive spoilage by B. sporogenes. Bacillus sporogenes is a 
common organism, and, according to Burke 4 and Meyer, 5 B. hotu- 
linus is more abundant than has heretofore been believed. This 
makes it all the more imperative that methods of canning shall be 
such as to eliminate, as far as possible, spoilage by these organisms, 
especially that of the toxin-producing B. hotulinus. 

DISCUSSION OF RESULTS. 

The use of canning powder is further complicated by the physio- 
logical factor of taste. Those who have condoned the use of such 
powder in canning have put forth the argument that the small 
amount of antiseptic present in a quart of food is no more harmful 
than the use of the common condiments which are also poisonous in 
quantity. They have failed to emphasize the fact that condiments 
by their taste alone give ample warning to the consumer long before 
a poisonous concentration is reached. There was practically no in- 
dication, however, of the presence of boric-acid canning powder in 
the foods canned in the bureau. Various members of the microbio- 
logical laboratory tasted product after product. They were aware, 
of course, that some contained the powder and so were more critical 
than they might haA^e been otherwise. Even for them it required 
close attention to detect the presence of the powder in any of the 

* Burke, G. S. The Occurrence of Bacillus Botulinus in Nature. J. Bad., t (1919) : 
541-553. 

5 Meyer, K. F., and Geiger, J. C. The Distribution of the Spores of B. Botulinus in 
Nature. Public Health Reports, 36 (1921) : 4. 



10 Department Circular 237, U. S. Dept. of Agriculture. 

samples. The consumer has no protection against the use of an ex- 
cess of the powder except the slight change in acidity, which becomes 
evident only when the excess is marked. There is, therefore, no com- 
parison to be made between condiments and the boric-acid canning 
powder in this respect. 

These experiments contribute little toward the controversy as to 
the effect of boric acid upon the consumer, although, in collaboration 
with the Bureau of Animal Industry, products canned with the 
boric-acid canning powder were shown to be deleterious to chickens 
(reported elsewhere). 

No claim of food or condimental value has ever been made for 
boric acid. Antiseptic power and harmlessness in the amounts used 
are its sole claims to a place in any food product. Analyzed on the 
basis of these experiments, the antiseptic power of boric acid has not 
proved great. What antiseptic power it has may be due either to its 
influence upon acidity or to the selective effects of the boron com- 
pound upon microorganisms. Kuhl, 6 Tanner and Funk, 7 Lazarus, 8 
and others have also reported feeble antiseptic powers for boric acid. 

To determine the relation of the canning powder to acidity the 
hydrogen ion concentration of the media used, both with and without 
the powder, was determined by the colorimetric method. In the 
test-tube experiments the dextrose agar had a pH value of 7 without 
the canning powder and of 6.5 with the canning powder. Milk had 
a pH value of 6.5 before the addition of the powder and of 6 after- 
wards. The pH value of wort broth was 5 without the powder and 
4.5 with it. The acidities of the fruits and vegetables used in the 
canning experiments are shown in Table 3. 

Table 3. — pH values a of products canned. 



Product. 


Series 1 
(method 

recom- 
mended, 

using 
canning 
powder). 


Series 2 
(method 

recom- 
mended, 
omitting 
canning 
powder). 


Series 3 
(cold- 
pack 
method). 


Product. 


Series 1 
(method 

recom- 
mended, 

using 
canning 
powder). 


Series 2 
(method 

recom- 
mended, 
omitting 
canning 
powder). 


Series 3 
(cold- 
pack 

method). 




4.0 
3.5 
3.5 
4.0 
5. 0-5. 5 
5.5 
6.5 


4.5 
4.0 
(") 
4.5 
6.0-6.5 
6.0 
7.0 


4.5 
5.0 
4.5 
4.5 
6.0 
6.5 
6. 5-7. 


Peas 


5. 0-5. 5 
3. 5-4. 
5.0 
4.5 
3.5 
3.5 


(M 
4.0 
5.5 
5.5 
4.0 
4.0 


6. 0-6. 5 




Rhubarb 


4.0 


Pears 


String beans 

Tomatoes 


6.5 




5.0 


Asparagus 


Cucumber salad — 
Mincemeat 




Lima beans 







a Determined for uninoculated jars at time of bacteriological examination. 



t> None canned. 



6 Kuhl, H. Boric Acid as a Preservative. Pharm. Centr., 50 (1900) : 550-561. 

7 Tanner, F. W., and Funk, R. S. Some Observations on the Use of Boric Acid as a 
Disinfectant. Am. J. Pharm., 91 (1919) : 206-210. 

8 Lazarus, A. Die Wirknngsweise der gebrauchlicheren Mittel zur Conservirung der 
Milch. Zts. Hyg., 8 (1800) : 207-239. 



A Boric-Acid Canning Powder. 11 

From these figures it is evident that the boric-acid canning powder 
in the amounts prescribed produces a slight but measurable increase 
in acidity. Bigelow and Cathcart, 9 Weiss, 10 and others have tested 
the relation of acidity as measured in this way to the effectiveness 
of processing temperatures. Increase in acidity has been shown to 
be a factor in bacterial destruction great enough to assist materially 
in sterilizing. The experiments reported here, however, indicate 
with equal clearness that the cooking prescribed for use with the 
powder was still inadequate to produce any large percentage of 
sterility product by product. 

In the cultural tests the canning powder introduced in the medium 
did restrain to a certain extent the yeast, certain molds, the non-spore- 
forming and some of the spore-forming aerobic bacteria. Since 
the molds and non-spore-forming bacteria, however, do not survive 
any standard cooking process, they appear in canned products only 
when totally inadequate processing periods and temperatures are 
used. In the authors' canning experiments these and the aerobic 
spore-forming bacteria do not appear as factors in loss. On the 
other hand, the spore-forming anaerobic organisms grew equally 
well in the presence of the canning powder in the test-tube and in the 
practical canning experiments. Manifestly neither the selective 
toxicity of the boron compound nor the increase in acidity as an 
aid in sterilization was adequate to prevent the loss. The group of 
organisms selected in these experiments included a series of strains 
of B. sporo genes, obtained in cases of extensive loss of canned food, 
and of B. botulinus, obtained from canned food responsible for food 
poisoning. The canning powder as used is seen, therefore, to fail 
entirely to protect the product against these two groups of organisms, 
which represent the most dangerous phase of spoilage in canned 
food. 

SUMMARY. 

The boric-acid canning powder in the amount recommended ex- 
erted a selective antiseptic action toward certain molds and members 
of the aerobic group of microorganisms in test-tube experiments. 
These groups are not responsible for spoilage in properly processed 
cans or jars, and may therefore be disregarded for the present pur- 
poses. The powder in the amount recommended for canning had no 
inhibitory effect on representative members of the anaerobic spore- 
forming group, especially the toxin-forming B. botulinus, which has 
recently been responsible for many deaths from food poisoning. 

9 Bigelow, W. D., and Cathcart, P. H. Relation of Processing to the Acidity of 
Canned Foods. National Canners' Assn. Research Laboratory Bull. 17-L (1921). 

10 Weiss, Harry. The Heat Resistance of Spores with Special Reference to the Spores 
of B. totulinus. J. Inf. Dis., 28 (1921) : 70-92. 



12 Department Circular 237, U. S. Dept. of Agriculture. 

In the practical canning experiments the use of the powder for 
acid products was shown to be an unnecessary and wasteful practice, 
since material packed without the powder kept as well as that packed 
with it. Its use with the more or less neutral vegetables showed 
that the powder plus the inadequate heating recommended was not 
sufficient to preserve the materials or to prevent the production of 
toxin in them by B. botulinus. 






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